The initial, preferential stimulation of proinsulin synthesis in isolated islets of Langerhans by glucose appears to involve certain elements of posttranscriptional control. In this project, it is proposed to 1) establish the regulatory role of glucose on total protein and proinsulin synthesis in cell-free lysates derived from highly purified preparations of pancreatic beta-cells, 2) establish the presence of a putative translational repressor activated in beta-cell lysates incubated in the absence of glucose, 3) isolate and characterize said translational repressor, and 4) investigate the mechanism of activation of the repressor. In order to study the effect of glucose on proinsulin synthesis, lysates prepared from purified beta-cells cultured in medium containing 20 mM glucose will be subjected to exclusion chromatography to obtain "glucose-free" lysates. It is predicted that this system will exhibit a dependence on glucose for maintaining sustained linear rates of total protein and proinsulin synthesis, and that in the absence of added glucose inhibition kinetics similar to those obtained in rabbit reticulocyte lysates incubated in the absence of added hemin will be obtained. These results would be compatible with modulation of proinsulin synthesis by glucose via a mechanism affecting the initiation of new polypeptide chains. Additional evidence to this effect will be obtained from the study of polysome profiles and of the ability of initiation factor fractions to reverse the inhibition of protein synthesis. Lysates incubated in the absence of glucose will be tested for the appearance of a repressor which will inhibit protein synthesis in glucose-supplemented lysates. The repressor will be isolated and characterized with emphasis in establishing that the observed inhibition of protein synthesis observed in lysates incubated in the absence of glucose is in fact mediated by the isolated repressor. Protein kinase activity of the repressor specific for an initiation factor and/or ribosomal protein will be investigated. Antibodies against the isolated repressor will be obtained from immunized rabbits. Finally, the inactive repressor will be purified and the mechanism responsible for its activation will be investigated.